1. Field of the Invention
The present invention relates to a material and a device, and more particularly to an electron transport material and an organic light emitting device.
2. Description of Related Art
With the development of science and technology, a flat panel display is the most focused display technology in recent years. An organic electroluminescent display is self-luminous, viewing-angle independent, power saving, simple in fabrication, and has a low cost, a low temperature operating range, a high response speed, and the full color. With these advantages, the organic electroluminescent display has a great potential in applications and might become the mainstream of the next generation flat panel displays.
The organic light emitting device includes an anode, an organic light emitting layer, and a cathode. The luminescence mechanism of the organic light emitting device is to inject a hole and an electron from the anode and the cathode to the organic light emitting layer, respectively. When the electron and the hole meet in the organic light emitting layer and recombine to form an exciton, so as to generate the phenomenon of light emission to emit a photon. Generally speaking, for an organic material, the conduction velocity of the electron is much smaller than the conduction velocity of the hole. Due to such a characteristic, the charge recombination region is close to the cathode and the probability of exciton quenching is increased.
To reach the balance between the electron and the hole in terms of the transport to facilitate that the exciton recombination region is located in the organic light emitting layer, in the organic light emitting device, an electron transport layer (ETL) including a material having a high electron transport velocity is usually disposed between the organic light emitting layer and the cathode. Generally speaking, the electron transport material needs to have the characteristics such as a suitable lowest unoccupied molecular orbital (LUMO) energy level, a high electron transport velocity, and a high glass transition temperature and thermal stability. As a triazine is a typical electron-poor heterocyclic system and has a high electron affinity, a desirable electron conduction velocity, and a simple synthesis method, for example, the 1,3,5-triazine derivative is widely used as the electron conduction material.
However, the current known 1,3,5-triazine derivative has a high LUMO energy level of about −1.93 eV to −2.08 eV, resulting in a large energy barrier when the electron is injected to the ETL from the cathode, thereby further affecting an initial voltage and an operating voltage of the device. Therefore, a proper electron transport material urgently needs to be developed in this field.